public class Fibonacci
{
    public void Run()
    {
        var input = Console.ReadLine();
        int x = int.Parse(input);
        int c = 1;
        int z = 1;
        int d = 0;
        int e = 0;
        for (int b = c; z < x-1; z++)
        {
            d = c + b;
            e = c;
            c = d;
            b = e;
        }
        Console.WriteLine(d);
    }
}